Small tanks that are conveniently sized to be carried and handled by hand are often filled with propane or butane fuel, and used by consumers for cooking, heating, torches, soldering, brazing, lighting, and the like. Such small tanks have a limited capacity, so they must be refilled or replaced with some frequency. Typically, such small tanks have a capacity of less than approximately three cubic feet. Safety is a serious concern in filling and refilling such tanks. Often, safety concerns with refilling dictate that such tanks must be provided fully charged with fuel, and the valves are configured so that they can not be refilled.
Typically, the valves in such small fuel tanks include a fill valve and a pressure relief or vent valve. The fill valve is often a conventional spring biased pin valve of the type that is often described as a Schrader valve. The same general type of pin valve is also used in great numbers, for example, as filling valves for bicycle and automobile tires. The fill valve is typically spring biased into the closed configuration. The fill nozzle is designed so that it forces the fill valve open against the spring bias when the fill nozzle engages the valve. Removing the fill nozzle allows the fill valve to close. Conventional vent valves provide for the safe venting of gas from a tank when the pressure within the tank exceeds the predetermined safe pressure limit for that particular tank. Conventional vent valves include a seal that is spring biased into the closed configuration. Pressure on the tank side of the valve will overcome the spring bias and open the vent valve when the pressure in the interior of the tank exceeds the predetermined safe pressure limit. Conventional vent valves generally vent directly out of the port in a direction that is axial with respect to the longitudinal axis of the vent port in which it is mounted. This tends to expose the user that is filling the port to a direct facially-aimed blast of gas when the vent valve opens. This presents a serious safety concern.
Typical conventional small tanks have the vent valve and the fill valve in separate ports. This increases the cost and complexity of such tanks. Also, the use of two ports increases concerns about safety and quality control. Where the tank is intended to be refilled by an end user, particularly where the refilling is accomplished from a larger tank, provisions must also be made for a dip tube. Tanks, for example, should not be filled with propane to beyond approximately 80 percent of the interior volume of the tank. Propane is typically a liquid at the pressures normally encountered by an end user in filling small tanks from larger ones. Thus, the tank should not be filled with liquid propane to more than 80 percent of its interior volume. Where the tank is in the form of a right cylinder the liquid propane level is a good indication of the percentage of the tank that has been filled. For a vertically positioned right cylindrical tank, a liquid level that is located at 80 percent of the length tank is a good indication that 80 percent of the volume of the tank is filled with liquid propane. A dip tube extends from the normally uppermost side of the tank for approximately 20 percent of the length of the tank into the tank's interior. The dip tube is hollow and it is vented directly to the ambient environment so that a user can see when liquid propane starts to run out of the dip tube port. This shows the user that the tank is full, and it prevents the tank from being overfilled. The dip tube is ported to the ambient environment so the end user can see liquid that is discharged from it. There are thus three ports, namely, a vent port, a fill port, and an overflow port that must be accommodated safely, reliably and inexpensively.
Accordingly, there exists a need for a simplified fill valve-vent valve design that is safe, simple, compact, reliable, and allows for refilling of small tanks by end users without special or expensive equipment. There is a need for the combination of fill and vent valves that can be installed in one port. Where refilling capability is provided there is a need for a dip tube to be incorporated in the same port as the two valves.